What should we add?

Low priority component of #9417.

Similar to #9419 for SabreSwap, it would be nice to bring all our available routing methods up-to-speed with control flow. See #9419 for more details on the current algorithm we have for routing control flow. Since LookaheadSwap is pure Python, its implementation would likely be very close to StochasticSwap's, and could hopefully re-use a lot of code.

This is low priority, since lookahead is a barely-used version of routing, and we're fairly sure it has latent bugs even in non-control-flow contexts.